Gusseted plastic bag



June 20, 1967 R. w. DICKSON 3,326,449

GUS SETED PLASTI C BAG Filed y 1965 2 Sheets-$heet 1 2 Sheets-Sheet 2 R. W. DICKSQN GUSSETED PLASTIC BAG June 20, 1967 Filed May 13, 1965 United States Patent 3,326,449 GUSSETED PLASTIC BAG Robert Walker Dickson, Welwyn Garden City, England,

assignor to British Visqueen Limited, Milihank, London, England, a corporation of Great Britain Filed May 13, 1965, Ser. No. 455,430 Claims priority, application Great Britain, May 13, 1964, 19,993/ 64 6 Claims. (Cl. 229-62) This invention relates to a new gusseted bag of plastic sheet material, and to a method of producing such bags.

Bags of plastic sheet material are frequently formed with re-entrant folds on each side, constituting side gussets separating the sides of the front and back panels of the bags, so that the bags are of substantially rectangular cross-section when filled, with square ends, and are thus more easily stacked than are simple fiat pillow bags after filling. A disadvantage of the gusseted bags when the mouths of the filled bags are required to be sealed by heat sealing is that the gusset folds must be sealed in with the side edges of the front and back panels, so that in the same seal there are four thicknesses of the sheet material at the sides of the seal and only two in the centre portion. This causes difficulty in heat sealing, because of the difficulty of sealing four thicknesses, particularly when the sheet is thick, and especially because points of weakness tend to be formed where the number of thicknesses changes. It is particularly difficult to form such seals after the bags have been filled, when they are clumsy to handle, and especially when the bags are formed of relatively thick sheet material, as for example in the case of sacks formed of heavy duty plastic film and suitable for the packaging of fertilizers and similar materials. It is also difficult to close the bags neatly by stitching after they have been filled, because of the problem of holding the gusset folds in position.

The present invention provides an open-mouthed bag of plastic sheet material comprising, in its flattened form: a front panel and a back panel; two side gusset panels folded between and joined to said front and back panels, each side gusset panel forming a fold with a re-entrant angle; at each side of the bag, in a position towards the mouth thereof, a seal joining together the front and back panels and the folded side gusset panel therebetween, said seal extending inwards at least as far as the re-entrant angle of the side gusset panel; and an open-mouth portion formed by parts of said front and back panels projecting beyond a line joining the points of intersection of said seals with the re-entrant angles of the gusset panels.

The seals are formed by heat sealing, generally by applying heat and pressure to the areas to be seamed, for example by means of resilient heat-sealing bars, or by dielectric heating.

The bag is preferably formed from gusseted tubular film of plastic material, in which the side gusset panels have been formed by inwardly folding a portion of the film at each side of the bag. It may, however, be formed from a flat sheet or sheets, suitably seamed and gusseted.

The present invention further provides a continuous method of making preferred forms of the bag of the invention. In these preferred forms, at each side of the bag the seal between the front and back panels and the side gusset panels joins a seal between the front and back panels only, the latter seal joining together the edges of the projecting mouth portion of the bag; these two seals may at each side of the bag be formed as a continuous seam, suitably curved or angled.

In accordance with this further feature of the invention, a continuous method of making open-mouthed gusseted bags from a length of plastic sheet material in a flattened tubular form, provided along each side with a gusset formed by a re-entran't fold of the tubing, comprises: advancing the length of tubing; forming a pair of substantially U-shaped heat seals opposite one another and one at each side of the tubing, each of said seals joining together the two opposed layers of the tubing and the infolded gusset therebetween, the arms of each said seal extending to the edge folds of the tubing and the base of each seal extending beyond the re-entrant angle of the gusset; forming a seal continuous with or adjacent to one pair of corresponding arms of said substantially U-shaped seals to provide a continuous seal extending across the whole width of the tubing; severing unsealed material from within said substantially U-shaped seals; severing or partially severing the tubing transversely across the neck formed in the tubing by said substantially U-shaped seals, at that end of the neck which is closer to the seal extending across the whole width of the tubing; advancing the length of tubing by the desired length of one bag; and repeating said sealing and severing steps.

The substantially U-shaped seals will hereinafter be referred to as U-shaped seals.

The tubing is preferably completely severed to give individual bags; but it may if desired be partially severed, for example by forming a line of slit perforations, and wound into a roll from which individual bags may subsequently be easily separated by tearing.

The sealing and severing steps may all be carried out at the same station and may be accomplished in varying order and in a varying number of stages. It is preferred, however, that the tubing be advanced by one bag length between the formation of seals by different sealing means. In a particularly preferred method of operation the length of tubing is advanced to a first sealing station, the pair of U-shaped seals is formed at this station, the tubing is then advanced by one bag length to bring the U-shaped seals to a second sealing station, and the seal across the whole or remaining width of the tubing is formed at the second sealing station while a further pair of U-shaped seals is formed at the first sealing station. The U-shaped seals may be made each by a single sealing operation, by means of a suitably shaped resilient sealing bar or similar sealing tool; or they may be made by two or more sealing steps. Unsealed material from within the U-shaped seals is preferably removed substantially simultaneously with the formation of the U-shaped seals, by means of a suitably shaped guillotine operated at the same time as the sealing bar. Preferably, the completed bag is severed from the length of tubing simultaneously with the forming of the sealing extending across the whole width of the tubing, that is, the bottom seal of the bag.

Preferred forms of the bag of this invent-ion and of the method for its production will now be described with reference to the accompanying drawings, in which:

FIGURE 1 represents a front view of the completed FIGURE 2 is a plan showing stages in the production of the bag; and

FIGURE 3 illustrates a second form of bag and its production.

In FIGURE 1 of the drawings: 1 represents the front panel and 1' the back panel of the bag, and 2 a side gusset panel; 3 is a seal joining the front and back panels with the side gusset panel therebetween, this seal extending to a point 4 beyond the re-entrant fold, 5, of the gusset, thereafter turning to a direction substantially parallel to the side of the bag and continuing to the mouth of the bag; 6 is the portion of the front panel of the bag that extends beyond a line joining 7, 7, the points of intersection of the seal 3 with the re-entrant folds of the gussets, to form, with the equivalent portion of the m9 back panel, the open mouth, 8, of the bag; and 9 is a continuous seal through all layers at the bottom of the bag. 10 is a reinforcing seal formed through the gusset, and extending a short distance beyond it, which is of course not essential to the bag of the invention but is formed when the bags are produced by a preferred method more particularly described with reference to FIG- URE 2.

In FIGURE 2 of the drawings: 11 represents the length of plastic sheet material in flattened tubular form, which advances intermittently by one bag length in the direction shown; 12 is one of the side gussets including a re-entrant fold of the tubing; 13 is one of a pair of U-shaped seals formed at the first sealing station, one at each side of the tubing, to join together the opposed layers of the tubing with the folded gussets therebetween; 14 is the cutting line for removal of unsealed material from within the U- shaped seal; 15 is the bottom seal of the bag, formed after the tubing has been advanced by one bag length to the second sealing station, this seal being in advance of the two U-shaped seals but adjacent to their leading arms; and 16 is the line across the neck formed in the tubing by the U-shaped seals, along which the completed bag is severed from the length of tubing, simultaneously with the forming of the bottom seal of the bag.

It is usually preferred to form the bottom seal of the bag beyond the U-shaped seals and adjacent to one pair of their arms, as shown in FIGURE 2. Those arms of the U-sh'aped seals, after the bag has been severed across its neck from the length of tubing, then form reinforcing seals across the gusset at the bottom corners of the bag, beyond the bottom seal. The bottom seal may however be formed across the U-shaped seals, adjacent to their said arms, the reinforcing seals thus being inside the bottom seal of the finished b'ag. A bag formed in this way is shown in part in FIGURE 3 of the drawings, which also indi cates the method of making the bag.

In FIGURE 3: 17 represents the length of sheet material in flattened tubular form; 18 is a side gusset; 19 is a U-shaped seal formed at the first sealing station; 20 is .the cutting line for removal of unsealed material from within the U-shaped seal; 21 is the bottom seal of the bag, formed after the tubing has been advanced by one bag length to the second sealing station, this se'al being formed across the U-shaped seals and adjacent to their leading arms; and 22 is the cutting line across the neck of the bag. It will be seen that the cutting line 20 along which unsealed material is cut from within the U-shaped seal allows material for the bottom seal, 21, of the bag to be continued to the edges of the length of tubing, to form the reinforcing seals.

Although the U-shaped seals are shown in the drawings as continuous seals, it is permissible for the seals to be interrupted at one or more points, provided that such interruptions do not have undesirable effects on the desired properties of the bag when finally sealed. For example, the seals may be interrupted anywhere in the portion beyond that destined to form the neck of the finally sealed bag, without impairing the weatherproofing of the filled bag. Indeed, it is advantageous to provide a short interruption in each seal over the point where they intersect the line along which the tubing is to be severed or partially severed transversely for separation of the individual bags, since this facilitates severing and prevents any damage to the seal by the severing step.

It will be appreciated that many other modifications may be made in the bags and methods particularly described. It is strongly preferred that the seals between the side gusset panels and the front and back panels be continued substantially to the mouth of the bag, for example as shown in FIGURE 1 and as produced by the method of the invention, or that they join separate seals formed at the sides of the mouth portion of the bag. But this is not absolutely essential to the bag of the invention, since the final seam closing the mouth of the filled bag may join the side gusset seals or be formed sufiiciently close -to them to prevent the leakage of material. The side gusset seals if continued to the bag mouth may curve or otherwise continue towards the mouth without turning through a sharp angle as shown. Moreover, the initial portions of said seals need not be formed at right angles to the side folds of the bag; preferably, however, they are either at right angles to or form an obtuse angle with the side folds of the bag. It is also preferred that in the bags formed by the method particularly described the seal or seals at the bottom of the bag be substantially at right angles to the sides of the bag. Thus, at least these arms of the U-shaped seals are preferably formed substantially at right angles to the side folds of the bag; it will be appreciated however that the U-shaped seal applied in the method described may other-wise often depart quite considerably from the exact U-shaped form.

By a further modification of the invention, the bottom seal may be formed merely by sealing across the bag between the said arms of the U-shaped seal, to form a single continuous seal; it is usually preferred, however, to form the reinforcing seals as described.

In other modifications of the method of the invention, the U-shaped seals may be formed in more that one step. Thus, for example, a pair of seals in the form of L-shaped angles or curves may be made by a first sealing step to form one side and the base of the U-shaped seals, and a second seal formed to extend across the whole width of the tubing, joining or crossing the L-shaped seals at or towards their inner ends, to provide at the $311116 time the second arms of the U-shaped seals and the seal across the remaining width of the tubing. Here again no reinforcing seals are formed, but these may be added at the same time as the second seal or by a further sealing step if desired.

It will, of course, be appreciated that, in any of the methods described, the mouth of the bags may be formed at the trailing end of the bag unit instead of at the leading end; the bottom seal of the bag is then formed between or adjacent to the other pair of arms of the U-shaped seals.

As indicated hereinbefore, the bags of the invention may be formed by methods other than that particularly described; for example they may be made from tubing formed by seaming a flat sheet, or from individual tubular units.

The particular advantage of the bag of this invention is that the seals joining together the side gusset panels and the front and back panels are formed during manufacture of the bag and thus under carefully controlled conditions. The user of the bag, after filling it, merely has to seal together the sections of the front and back panels forming the open mouth of the bag; and because the mouth of the bag projects, this is essentially equivalent to sealing the mouth of an ordinary pillow bag, presenting no difficulty. The amount of projection of the mouth of the bag may be designed to suit the particular type of sealing machine that is to be used for sealing the filled bags. For example, in a 37 /2 inch long sack intended to be sealed by a conventional band sealing machine, the mouth is suitably from 1 /2 to 2 inches deep. Material used in forming the bag and projecting beyond the seals formed between the front, back and gusset panels, and sideways beyond the mouth portion of the bag, is preferably trimmed off, as in the bag-making method particularly described, so that it does not interfere with the final sealing of the mouth of the bag.

Stitching methods for closing the mouths of the filled bags are preferably avoided because the stitching spoils the water-proof qualities of the bags. However, even where a stitching method is used an advantage is obtained, in that the need to hold the folded side gusset panels between the front and back panels, in stitching up the mouth of the filled bag, is avoided. The final closing of the filled bag thus becomes a much simpler operation.

Plastic sheet materials particularly suitable for making the bags of this invention include films of polythene, polypropylene or polyvinyl chloride. Each of these plastics can be formed into films having high resistance to water, adequate strength even for sacks for containing heavy materials such as fertilizers and chemicals, and of sufiiciently low cost to allow bags to be produced reasonably cheaply. Polythene and polypropylene films are best sealed by the application of heat and pressure from a hot tool, While polyvinyl chloride film may conveniently be sealed either by the same method or by dielectric heating. Pre-heating of the film in the area of the outer and/ or inner layers of the gusset assists the formation of strong seals.

The invention is particularly useful in its application to the production of heavy duty sacks from plastic film, of the type used for the packing of, for example, fertilizers, chemicals, and plastic granules and powders.

I claim:

1. An open-mouthed bag of plastic sheet material comprising, in its flattened form: a front panel and a back panel; two side gusset panels folded between and joined to said front and back panels, each side gusset panel forming a fold with a re-entrant angle; at each side of the bag, in a position towards the mouth thereof, a seal joining together the front and back panels and the folded side gusset panel therebetween, said seal extending inwards beyond the re-entrant angle of the side gusset panel; and an open-mouth portion formed by only parts of said front and back panels projecting beyond a line joining the points of intersection of said seals with the re-entrant angles of the gusset panels, said open-n1outh portion having only a constant number of layers of material throughout its entire width, whereby the open-mouth portion may be completely sealed in a single step and without interference from a changing number of layers of material across the width of the bag.

2. A bag as claimed in claim 1 in which, at each side of the bag, the said seal between the front and back panels and the folded side gusset panel joins a seal between the front and back panels only, the latter seal joining together the edges of the projecting mouth portion of the bag.

3. A bag as claimed in claim 2 in which the two seals are formed as one continuous angular seal.

4. A bag as claimed in claim 1 in which the closed end is closed by a continuous seal across the width of the bag and reinforcing seals are provided adjacent thereto extending inwards from each side of the bag at least as far as the re-entrant angle of the gusset panel.

5. A bag as claimed in claim 1 formed from a length of gusseted tubular film of plastic material.

6. A bag as claimed in claim 1 in which the plastic sheet material is selected from the group consisting of polythene and polypropylene.

References Cited UNITED STATES PATENTS 2,265,075 12/1941 Kneutter 93-35 2,749,020 6/1956 Baxter 229-53 2,790,591 4/1957 Rosen 22953 2,990,101 6/1961 Mead et al 22953 3,077,820 2/1963 Been 9335 3,143,277 8/1964 La Fleur 229-57 3,186,625 6/1965 Mead et al. 229-53 FOREIGN PATENTS 615,653 2/1961 Canada.

JOSEPH R. LECLAIR, Primary Examiner. D. M. BOCKENEK, Assistant Examiner. 

1. AN OPEN-MOUTHED BAG OF PLASTIC SHEET MATERIAL COMPRISING, IN ITS FLATTENED FORM: A FRONT PANEL AND A BACK PANEL; TWO SIDE GUSSET PANELS FOLDED BETWEEN AND JOINED TO SAID FRONT AND BACK PANELS, EACH SIDE GUSSET PANEL FORMING A FOLD WITH A RE-ENTRANT ANGLE; AT EACH SIDE OF THE BAG, IN A POSITION TOWARDS THE MOUTH THEREOF, A SEAL JOINING TOGETHER THE FRONT AND BACK PANELS AND THE FOLDED SIDE GUSSET PANEL THEREBETWEEN, SAID SEAL EXTENDING INWARDS BEYOND THE RE-ENTRANT ANGLE OF THE SIDE GUSSET PANEL; AND AN OPEN-MOUTH PORTION FORMED BY ONLY PARTS OF SAID FRONT AND BACK PANELS PROJECTING BEYOND A LINE JOINING THE POINTS OF INTERSECTION OF SAID SEALS WITH THE RE-ENTRANT ANGLES OF THE GUSSET PANELS, SAID OPEN-MOUTH PORTION HAVING ONLY A CONSTANT NUMBER OF LAYERS OF MATERIAL THROUGHOUT ITS ENTIRE WIDTH, WHEREBY THE OPEN-MOUTH PORTION MAY BE COMPLETELY SEALED IN A SINGLE STEP AND WITHOUT INTERFERENCE FROM A CHANGING NUMBER OF LAYERS OF MATERIAL ACROSS THE WIDTH OF THE BAG. 